A variety of assays include using an electrochemical sensor to detect the presence and/or amount of an agent in a biological sample. Biological samples generally contain compounds in addition to the agent. These compounds are often a source of noise in the results of using the electrochemical sensor. The quality and reliability of these results can be improved by reducing this noise. The noise can be reduced by preparing a sample before using the sample with the sensor. As a result, there is a need for methods and/or system that can be used prepare samples before assays.